The Gmail app on iPhone is rendering text far smaller than on Android or iPad. It seems that Gmail on iPhone is ignoring font-size rules (or is rendering text very differently), even when rules are in inline CSS.

Here is a stripped down version of the HTML:

    <table border="0" cellpadding="0" cellspacing="0" height="100%" width="100%" id="mainTable">
        <tr>
            <td align="center" valign="top">
            <table border="0" cellpadding="0" cellspacing="0" width="100%">
                        <tr>
                           <td align="center" valign="top" id="templateBody">
                                   <table border="0" cellpadding="0" cellspacing="0" width="600" class="templateContainer">
                                        <tr>
                                           <td valign="top" class="bodyContent" style="-webkit-text-size-adjust:none;font-size:13px;">
                        <p style="margin:1em 0; font-size:13px;">Content goes here</p>
                                           </td>
                                       </tr>
                                    </table>
                             </td>
                          </tr>
                </table>
            </td>
        </tr>
    </table>

On iPad and on Android devices, this works -- the text is a legible 13px. On iPhone (tested on iPhone 4S and iPhone 5S, iOS 7 & 8), however, the text is unreadably small. Same thing with font-size:1em; and font-size:1rem. Adding a 600px x 1px image outside the <table> doesn't fix the problem. How does one get Gmail fonts to render at the same size across all Gmail platforms? Kind of at a loss since there's no media query support.